Unsaturated polyester resins are well-known in the art. The unsaturated polyester resins are used to form thermoset resin compositions which are especially useful in various molding processes. In particular, the reaction injection molding (RIM) process uses such thermoset resin compositions to make resin-reinforced fiberglass structures for use in automobile applications. The unsaturated polyester resins are generally the poly condensation products of di- or poly-carboxylic acids or their anhydrides and di- or poly-hydroxylated alcohols or alkylene oxides. The unsaturated polyester resins are usually crosslinked through their double bonds with a compatible monomer also containing ethylenic unsaturation. The cross-linked resins are thus thermosetting and when fully cured are insoluble and infusible. For example, the Dunnavant et al., U.S. Pat. No. 4,374,229 assigned to the Ashland Oil Co., discloses moldable, reactive acrylic resins based on oligomeric polyesters which are structurally linked through a urethane residue. The Dunnavant et al. composition contains polyester segments containing internal ethylenic unsaturation terminally joined to one another through polyurethane linkages. Each of the polyester segments possess end groups containing vinyl unsaturation. The compositions are copolymerized with a vinyl or polyallyl crosslinking agent.
However, Dunnavant et al. does not suggest the achievement of low viscosity, aminated, hydroxylated, polyester resins which are compatible with isocyanate and which have an increase in functionality due to additional hydroxyl groups incorporated into the resin backbone and yet do not require the use of a vinyl crosslinking agent.